The polyphenylene ether resins are a family of engineering thermoplastics that are well known to the polymer art. These polymers may be made by a variety of catalytic and non-catalytic processes from the corresponding phenols or reactive derivatives thereof. By way of illustration, certain of the polyphenylene ethers are disclosed in Hay, U.S. Pat. Nos. 3,306,874 and 3,306,875, and in Stamatoff, U.S. Pat. Nos. 3,257,357 and 3,257,358. In the Hay patents, the polyphenylene ethers are prepared by an oxidative coupling reaction comprising passing on oxygen-containing gas through a reaction solution of a phenol and a metal-amine complex catalyst. Other disclosures relating to processes for preparing polyphenylene ether resins, including graft copolymers of polyphenylene ethers with styrene type compounds are found in Fox, U.S. Pat. No. 3,356,761; Sumitomo, U.K. Pat. No. 1,291,609; Bussink et al, U.S. Pat. No. 3,337,499; Blanchard et al, U.S. Pat. No. 3,219,626; Laakso et al, U.S. Pat. No. 3,342,892; Borman, U.S. Pat. No. 3,344,166; Hori et al, U.S. Pat. No. 3,384,619; Faurote et al. U.S. Pat. No. 3,440,217; and disclosures relating to metal based catalysts which do not include amines, are known from patents such as Wieden et al, U.S. Pat. No. 3,442,885 (copper-amidines); Nakashio et al, U.S. Pat. No. 3,573,257 (metal-alcoholate or -phenolate); Kobayashi et al. U.S. Pat. No. 3,445,880 (cobalt chelates); and the like. In the Stamatoff patents, the polyphenylene ethers are produced by reacting the corresponding phenolate ion with an initiator, such as peroxy acid salt, an acid peroxide, a hypohalite, and the like, in the presence of a complexing agent. Disclosures relating to non-catalytic processes, such as oxidation with lead dioxide, silver oxide, etc., are described in Price et al. U.S. Pat. No. 3,382,212. Cizek, U.S. Pat. No. 3,383,435 discloses polyphenylene etherstyrene resin compositions. All of the above-mentioned disclosures are incorporated by reference.
The term "polystyrene resin" includes polymers and copolymers of styrene, alpha methyl styrene, chlorostyrene, and the like.
The term "EPDM" includes rubbery interpolymers of a mixture of mono-olefins and a polyene. Preferred types are those rubbery interpolymers of ethylene, an alpha-olefin, and a polyene. Rubbery interpolymers of ethylene, propylene, and a polyene are especially preferred.
In the prior art, rubber-modified styrene resins have been admixed with polyphenylene ether resins to form compositions that have modified properties. The Cizek patent, U.S. Pat. No. 3,383,435, discloses rubber-modified styrene resin-polyphenylene ether resin compositions wherein the rubber component is of the unsaturated type such as polymers and copolymers of butadiene. The physical properties of these compositions are such that it appears that many of the properties of the styrene resins have been upgraded, while the moldability of the polyphenylene ethers are improved.
Nakashio et al, U.S. Pat. No. 3,658,945 discloses that from 0.5 to 15% by weight of an EPDM-modified styrene resin may be used to upgrade the impact strength of polyphenylene ether resins. In Copper et al, U.S. Pat. No. 3,943,191 it is disclosed that when the highly unsaturated rubber used in compositions of the type disclosed by Cizek, is replaced with EPDM-rubber that has a low degree of residual unsaturation, the thermal oxidative stability and color stability are improved. The EPDM rubber in the Copper et al compositions is comprised substantially of particles in the range of 3-8 microns.
The impact strength of the Copper et al compositions is superior to that of a polyphenylene ether resin alone or that of similar compositions comprised of unmodified polystyrene; however, the impact strength of the Copper et al. compositions is inferior to that of similar compositions comprised of polystyrene modified with polybutadiene rubber, such as a composition known as FG-834, available from Foster-Grant Co. As is disclosed in U.S. Pat. No. 3,981,841, the impact strength of the Copper et al compositions can be improved by incorporating therein impact modifiers such as an emulsion-grafted EPDM polystyrene copolymer. U.S. Pat. No. 4,152,316, incorporated herein by reference, discloses that a composition of a polyphenylene ether resin and an alkenyl aromatic resin modified with an EPDM rubber comprised of particles having a median diameter less than about two microns, preferably about 0.5 to 1.5 microns, is a very useful thermoplastic molding material having good thermal oxidative stability and good room temperature impact strength but inferior low temperature impact strength.
In U.S. Pat. No. 4,102,850 it is disclosed that the addition of a small amount of mineral oil to the polymerizing mixture of styrene and EPDM rubber produces EPDM-modified polystyrene which yields blends with polyphenylene oxide having significantly better low-temperature impact strength than blends made from EPDM-polystyrene made without the mineral oil.
In U.S. Pat. No. 3,737,479 it is disclosed that the addition of silicone oils to polyphenylene oxide or to polyphenylene oxide-polystyrene blends improves Gardner impact strength but does not affect the Izod impact strength.
In U.S. Pat. No. 4,226,761 there is disclosed a composition of a polyphenylene ether resin and an alkenyl aromatic resin that is modified with a polysiloxane in the form of small rubber-like particles. In column 4, lines 44-55 it is stated that some of the R groups, in the formula of the polysiloxane "must be capable of (1) grafting to an alkenyl aromatic resin during polymerization and (2) forming crosslinks so that the final product contains discrete rubbery particles comprised of the polysiloxane and polysiloxane graft polymer, with occlusion of alkenyl aromatic resin in a matrix of an alkenyl aromatic resin such as polystyrene. Therefore, at least some of the R groups, preferably at least one percent, are selected from the group of unsaturated hydrocarbons . . . such as vinyl, allyl, and cyclohexenyl groups."
It has now been found that when small amounts of a silicone oil which is free from unsaturated hydrocarbon groups are added to an EPDM rubber and a styrene monomer reaction mixture, before or during polymerization of the styrene, the resulting product can form blends with a polyphenylene ether resin, which after molding have substantially better room temperature properties (Izod impact, Gardner impact, and surface appearance, gloss) than blends with EPDM-polystyrene made with no modifier or with aliphatic mineral oil. Other properties of the blends, such as ductility, tensile strength and heat distortion temperature (HDT), were not adversely affected. Low temperature impact strength, both Izod and Gardner, was also improved.
It has also been found that the improved molding compositions can be combined with reinforcing fillers of various kinds and flame-retardants.
In U.S. Pat. No. 4,226,761 the blends of polyphenylene ether resin are with graft copolymers of styrene and polysiloxane. Among the differences of the compositions of the patent and the compositions of the present invention, is that, as pointed out in the patent, the polysiloxane in the patent must contain some unsaturated hydrocarbon groups so that the polysiloxane grafts with the styrene and becomes the rubber phase in the polystyrene resin. In the compositions of the present invention the silicone oil is free from any unsaturated hydrocarbon groups, and simply modifies the properties of the polystyrene containing EPDM rubber particles. It may be largely in the rubber phase, but is not chemically bonded to either the polystyrene or the EPDM rubber.
Also, in the patent, the polysiloxanes employed are the high molecular weight polymers (column 4, lines 7 and 8), and in Example 1, therein, the "polysiloxane used was a high molecular weight gum", in contrast to the silicone oil, a fluid, which is the subject of the present invention.